Spark plug



Sept. 24, 1929. w, DUBlLlER 1,729,248

SPARK PLUG Filed Aug. 13, 1927 INVENTQR BY William Dubiher ATTORNEY Patented Sept. 24, 1929 UNITED STATES PATENT OFFICE WILLIAM DUIBILIER, OF NEW ROCHELLE, NEW YORK, ASSIGNOR TO RADIO PATENTS CORPORATION, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK SPARK PLUG Application filed August 13, 1927, Serial No. 212,643, and in Germany October 27,-1926.

My invention relates to the construction of spark plugs for use in internal combustion engines in which the spark discharge gap may be regulated by automatic means during varying conditions of operation. Moreover, the invention relates to the provision of limits or stops .for insuring reliability of operation of the means employed to bring about the automatic regulation of the spark gap distance.

It is a well known fact that electric ignition in internal combustion engines depends almost entirely upon the load that the machine is under, or upon the temperature of the engine. The ignition is especially difiicult when starting because the gas mixture is drawn into cold cylinders without having been warmed by any preceding explosions, that is, has not been pre-heated. Ig-

nition is very easy in a hot machine, for example, one that has been running for some time or is under a full capacity load.

When a machine is cold or lightly loaded, that is, when. the gas mixture is cool, if the spark distance is fixed as usual, ignition is very diflicult and may not take place at all. The usual gap distance, with a warm or hot gas mixture, offers a very small resistance to the penetration of a spark so that the current crossing the gap is excessive and may bring the electrodes to a glowing heat. If this happens, injurious pre-ignition results since the gas mixture will be ignited by the glowing electrodes before the compression is completed. Such excessive heating of electrodes would result that the machine would have to be stopped to allow the glowing electrodes to coo The object of this invention is to overcome these conditions by having the spark distance between the electrodes made variable so that this distance is dependent upon the working conditions of the engine. The spark distance is small while the machine is cold, as is the case when running under a light load, and becomes greater as the engine becomes warmer and more heavily loaded. A suitable automatic variation of the spark gap is made dependent on the loading conditions by belng determined by the temperature of-the engine.

With such an arrangement it can easily be brought about that the sparking resistance, or resistance to ignition will remain approximately constant under all conditions, for although the conductivity of a hot mixture is in excess of a cold one, the sparking distance is also correspondingly increased.

In particular the invention consists of making' at least one electrode movable, and this movable electrode is so built or held that the sparking distance'increases as the engine becomes warmer. In the simplest form such an action of the electrode can be brought about by placing it on the end of a bimetallic stri. or supporting it by such strip, and if this b1- metallic element lies in the combustion chamber its form will change with increasing tem-' perature so that the distance between electrodes increases, while with falling temperature this distance decreases.

The invention is illustrated by an example, but not limited to it, any spark gap may be similarly changed.

Fig. 1 is a side elevation of a spark plug provided with this improvement, and

Fig. 2 is a bottom plan or end view of the spark plug shown in Fig. 1.

As is usual, the electrode in the middle of the plug passes in a well known manner through a piece of insulation, such as porcelain, and one branch of the circuit is attached at the to by means of a clamp or thumbscrew. onnection to the other branch of the circuit is made by means of the fastening of the main portion of the spark plug shell to the cylinder-head of the engine by the customary screw-thread 2. The central electrode 5 is located in the insulating body of porcelain 3, while the main shell 4, in the modification illustrated, carries two electrodes 6 and 8. The one electrode 8 is rigidly fastened to the shell or main body of the spark plug and is suitably spaced from the middle electrode 5 so as to obtain the most eflicient sparking for a hot, fully loaded engine. The other electrode 6 has one end rigidly attached to the shell4 of the plug and consists of a bimetallic stri that is shown in the drawing spaced from t e middle electrode 5 at that particular distance which is most eflicient for starting purposes or for running when the engine is cool.

The movable end of this bimetallic strip 6 contacts with the end of the fixed electrode 8 when the engine is cool or lightly loaded. This contact 8 forms a limit or stop, reventing the small distance between mova le electrode 6 and central electrode 5 from ever going below a certain minimum distance Whichis much less than the conventional spark gap setting and this minimum distance is the one that is most suitable for the starting of a cold engine or the operation of a very lightly loaded one. Moreover this stop 8 makes it impossible for any short circuit to occur between 5 and 6. As soon as the engine is started and the engine becomes warm the strip 6 also is heated up. The two metals used in forming this strip are so chosen and arranged that the strip 6 under the influence of heat moves away from the end of the electrode 8 and gradually increases the distance between the strip 6 and the middle electrode 5. As soon as the engine becomes fully heated or is placed under a full load, the spark distance between the strip 6 and middle electrode 5 may, and preferably should, become greater than the distance between the fixed electrode 8 and the central electrode 5. But as soon as this happens, the spark will cease travelling from 5 to 6 and will spring across the gap from the central electrode 5 to the stop 8.

Numerous advantages result from this arrangement, for example, in case an engine runs much of its time under full load the spark will then pass most of the time between the fixed electrodes 5 and 8 and the less robust bimetallic element will be relieved from pitting and local distortion due to the spark always passing to one point on the bimetallic element. Or, the expense of fastening a special heat resistive point to the bimetallic element will be obviated. Furthermore, if difficult working conditions and the continuous expansion and contraction of the bimetallic element should cause it to permanently set or permanently take on a form more curved or straighter than when it was new, the limit or stop electrode 8 would insure that 'it would never short-circuit at the central electrode 5 whencold, and could never stop the engine through setting up an excessive gap distance in case it straightened out too much while hot, for then the spark would spring from the elect-pode 5 to the stop 8.

Should a cooling of the engine occur for any reason, then the thermally sensitive element 6 will creep closer to the central electrode 5 tillthe distance between 5 and 6 becomes less than the distance between 5 and 8 and the spark will then resume its path between 5 and 6. If the engine'is stopped, or if the cooling continues due to the load becoming extremely light, then the bimetallic band will actually contact with the end of stop 8,

thereby reestablishing the minimum distance mentioned earlier in the description.

It is self-evident that this invention can be applied to any standard spark plug without altering or changing any of the major parts of the same. Numerous changes in the modification illustrated can be made; for example, the bimetallic element 6 need not be bimetallic its entire length, but could have the outer end where the spark occurs made of some high melting point metal, such as tungsten iron, or even pure tungsten.

The fixed electrode in like manner can be formed in various ways and made in whole or in part of a metal of high melting point.

Instead of having the spark pass part of the time to a fixed and part of the time to a movable electrode, it could be arranged to have it pass all the time to the movable electrode and in that case it would. be desirable to have a stop to limit the maximum spacing of the spark gap as well as to limit the minimum opening of the gap.

Also it is not essential to have just one fixed centralielectrode, but there. could even be a plurality of electrodes arranged eccentrically, and these arranged in the sense of this invention with one or more moving or respectively fixed electrodes.

The invention is not limited in detail to the single modification shown in the drawings and described above, but variations of structure are intended to be limited only by what:

I claim as my invention:

1. A spark plug having a fixed electrode, a thermally responsive movable electrode and a stop for the movable electrode, said stop and said movable electrode being located relative to each other so that the minimum spark gap distance is determined by the stop, said movable electrode, said fixed electrode and said stop being positioned with respect to each other in such a manner that the maximum spark gap distance is determined by the distance between said stop and said fixed electrode.

2. A spark plug having two electrodes, one of said electrodes being movable in accordance with temperature changes of the surrounding medium, and a stop for the movable electrode with metallic connectionto it located so as to limit the motion of such movable electrode toward the other electrode.

3. A spark plug having at least two electrodes, thermally responsive means associated with one of said electrodes adapted to move said electrode freely to determine the sparking distance between said electrode and another of said electrodes at any ordinary temperature, and means to limit the movement of said first-mentioned means positioned adjacent to said first mentioned means, to a minimum sparking distance at a low temperature.

4:. In a spark plug the combination of at least two electrodes positioned with respect to each other, one of said electrodes being movable with respect to another one of said electrodes in accordance with the temperature thereof whereby the air gap between said last mentioned electrodes is varied, and means positioned adjacent to said movable electrode for governing the minimum length of said air gap.

5. A spark plug having an electrode movable in accordance with temperature changes, a fixed electrode, said fixed electrode being insulated from said movable electrode, and a stop member, said stop member being electrically connected to said movable electrode,

said stop member being positioned adjacent.

to said movable electrode so that the maximum and minimum length of the spark gap of the spark plug is governed by said stop member.

In testimony whereof I have aflixed my signature.

' WILLIAM DUBILIER. 

